In a charged particle beam device such as represented by a scanning electron microscope, a sample is scanned with a narrowly converged charged particle beam, obtaining desired information (such as a sample image) from the sample. In such a charged particle beam device, resolution is becoming increasingly higher year by year, resulting in an increase in the observation magnification ratio required for the high resolution. Beam scan methods for obtaining the sample image include a method where a plurality of images obtained by high speed scan are integrated to obtain a final target image, and a method where a target image is acquired by a single low speed scan (image capture time for one frame on the order of 40 msec to 80 msec). As the observation magnification ratio is increased, the influence of drift of the field of view on the acquired image becomes more serious. For example, in the method where the target image is acquired by integrating the image signals obtained by high speed scan on a pixel by pixel basis (frame integration), if there is a drift during image integration due to a charge-up or the like of the sample, pixels with a displaced field of view would be integrated, resulting in the target image after integration being blurred in the drift direction. In order to decrease the influence of drift, the number of integrated frames may be decreased so as to shorten the integration time; however, this makes it difficult to obtain a sufficient S/N ratio.
In the method where the image is acquired by low speed scan, if there is a drift during image capturing, the image would be deformed by the flow of the field of view in the drift direction.
When a resist pattern with high sensitivity is irradiated with charged particles by a charged particle beam device, the resist may be shrunk (contracted) by the scientific attributes of the resist. In the aforementioned method where the final target image is acquired by integrating a plurality of images obtained by high speed scan, if the shrinking occurs during image integration, pixels with a displaced edge position due to the shrinking would be integrated, resulting in a blurring at the edge of the target image after integration.
Patent Literature 1 discloses a technology where image deformation or position displacement due to a drift in a plurality of images obtained by the plurality of scans is detected by image matching, and a composed image in which the position displacement is corrected based on the detected image deformation or position displacement is generated.